A friction stir welding method is a technique in which, while a tool is rotated, a probe installed at the leading end of the tool is inserted into workpieces and, then plastic flow resulting from frictional heat occurring between the rotating tool and the workpieces due to movement of the rotating tool is used to weld the workpieces.
The friction stir welding method is advantageous in that a joint part is not melted by high heat during welding and, therefore, the workpieces are not distorted or deformed.
Techniques for enhancing the welding reliability of friction stir welding includes, for example, the techniques described in Patent Documents 1 and 2.
In friction stir welding, when a probe is withdrawn at a probe end point position where a joint end point in a joint part is formed, a probe withdrawing hole is left in the vicinity of the joint end point. Also, the welding reliability remains uncertain in the vicinity of the joint end point. Therefore, in the techniques disclosed in Patent Documents 1 and 2, after the probe has been moved to the probe end point position, the probe is not immediately withdrawn at this position but the probe is moved to a position away from the probe end point position and, then, the probe is withdrawn. In the above-described technique, the probe is withdrawn at a position away from the probe end point position, by which the probe withdrawing hole is placed away from the joint end point to improve the welding reliability in the vicinity of the joint end point.